Recently, the general trends in designing electronic devices are toward small size, light weightiness and easy portability. Moreover, with the increasing development of electronic industries, the internal circuitries of the electronic devices are gradually modularized. In other words, plural electronic components are integrated into a single circuit module. For example, a power module is one of the widely-used circuit modules. An example of the power module includes but is not limited to a DC-to-DC converter, a DC-to-AC converter or an AC-to-DC converter. After the electronic components (e.g. capacitors, resistors, inductors, transformers, diodes and transistors) are integrated as a power module, the power module may be installed on a system circuit board.
A conventional package structure of a power module will be illustrated as follows. Firstly, plural power semiconductor bare chips, plural passive components and plural pins are disposed on a first surface of a substrate. Through the pins, the power module can be connected with an external circuitry. In particular, the power semiconductor bare chips, the passive components and the pins are welded on the substrate via solder paste. Then, the power semiconductor bare chips, the passive components and the pins are connected with each other through conductive wires by a wire bonding process. Consequently, an exposed power module is produced. Moreover, the power semiconductor bare chips, the passive components and the pins of the exposed power module are covered by an inverted U-shaped covering member. The covering member has plural openings corresponding to the pins. The pins are penetrated through the corresponding openings and partially exposed outside the covering member. Meanwhile, the package structure of the power module is produced. Moreover, the exposed pins may be inserted into corresponding insertion holes of a printed circuit board. Moreover, a heat sink is attached on a second surface of the substrate, wherein the second surface is opposed to the first surface. In case that the power module is operated at a high voltage, a great deal of heat is generated. The heat sink attached on the second surface of the substrate can facilitate dissipating the heat to the surroundings.
However, since the heat sink is disposed on the second surface of the substrate, the heat of the power module is only able to be dissipated to the surroundings by a single side cooling mechanism. Moreover, since the covering member has higher thermal resistance and is not contacted with the heat sink, the covering member cannot provide a good thermal conduction path. In other words, the heat dissipating efficiency of the conventional package assembly is not satisfied.